Thermoanalytical sensors are used in suitably designed thermal analysis instruments for the determination of different properties and parameters of a sample that is subjected to changes in temperature.
Examples of state-of-the-art thermal analysis instruments include, among others, DSC (differential scanning calorimetry) instruments. DSC instruments are used to determine temperature-dependent changes in the chemical or physical properties of a sample, or rather of the material from which the sample was taken. This includes for example heat-flow measurements of exothermic or endothermic events accompanying a transition, such as for example a phase transition, as well as other effects occurring in a sample that is subjected to temperature changes. The changes taking place in the sample can be determined through comparison against a reference, wherein the latter can be either the unoccupied reference measurement position or a suitable reference material. Dependent on the type of DSC instrument, the reference material or the sample material can be placed on the respective measurement position either directly or in a suitable receptacle. Thermoanalytical sensors can also be employed in other instruments such as for example TGA-DSC instruments (wherein TGA stands for Thermo-Gravimetric Analysis), or HP-DSC (High-Pressure DSC) instruments, as well as in further instruments of the known state of the art.
Thermal analysis instruments are frequently run in a heat flux operating mode and in a power compensation operating mode.
In the power compensation mode, the power supplied to a heater and/or the power supplied to a compensation heater is controlled and regulated in such a way that the temperature difference between the reference position and the sample position is driven to zero. Based on the power needed for this compensation, it is possible to deduce the heat flow into the sample. In the ideal case, the spent power corresponds to the heat flow into the sample.
The heat flux principle is often used in thermal analysis instruments that have a common holder for the sample and the reference. The heat flow paths between the measurement positions and the heater should be known so that, ideally, any temperature differences between the two measurement positions are only the result of changes in the sample. Based on the real temperatures at the sample position and at the reference position, the heat flow rates can be calculated and quantitatively evaluated.
Thermoanalytical sensors for instruments of this type are often disk-shaped, with one surface carrying at least one measurement position that is connected to a temperature sensor unit which senses the temperature at the respective measurement position and/or the differential temperature between a sample position and a reference position. From a connected heater device, the sensor and the at least one measurement position associated with the sensor can be supplied with heat, in particular according to a suitable temperature/time program for the generation of temperature changes.
The known state of the art offers different types of such thermoanalytical sensors.
For example in F. X. Eder, Arbeitsmethoden der Thermodynamik, Band 2 (Working Methods of Thermodynamics, Volume 2), Springer Verlag 1983, page 240, a sensor is disclosed which includes a temperature sensor unit produced by thin-film vapor deposition on a substrate.
In DE 39 16 311 C2, a sensor is disclosed with a temperature sensor unit deposited on a substrate by using thick film technology methods.
These sensors have in common that the temperature sensor units have at each measurement position a plurality of thermocouples or thermal junctions that are formed directly on a sensor surface.
Sensors with temperature sensor units containing a plurality of thermocouples are also disclosed in EP 1 528 392 A1, DE 10 227 182 A1, DE 39 16 311 A1 and WO 2006/114394 A1. The sensors disclosed in these references have one or more measurement position, wherein the temperature sensor units have been deposited on the sensor surface by using different deposition techniques and/or different layout patterns, for example in order to increase the number of thermocouples at each measurement position, or to provide the capability of measuring temperature in more dimensions with an arrangement of thermocouples in several layers or planes of the sensor.
These sensors have in common that each measurement position is connected with a temperature sensor unit which is formed in this case in particular as a thermocouple arrangement deposited in thin film or thick film technology in a pattern surrounding the measurement position on the top side of a substrate. Each thermocouple arrangement is connected to an electronic circuit by way of an electrical contact pad and at least one suitable wire passing through the substrate. One end of the metallic wire, the upper end, is bonded from the top side of the substrate to the electrical contact pad of the temperature sensor unit in order to establish a materially integral connection in the form of a bonded joint between the electronic circuit and the temperature sensor, wherein with the fastening of each individual wire, a wire loop is created on the top side of the substrate.
The connection to the circuit by bonding the at least one metallic wire from above, i.e. from the top side of the sensor, with each wire forming a loop, has the disadvantage that it strongly limits the total number of connections or contacts that can be realized, as the space on the top side of the sensor becomes filled up with the wire loops. In addition, the wire loops can easily be damaged and/or torn apart, whereby the sensor becomes inoperative.
It is therefore an unmet object of the prior art to provide a particularly robust and user-friendly sensor which, in addition, is designed so that a multitude of contacts can be arranged on the top side of the sensor.